For obtaining oxygen on board aircraft, usually air fractionization installations are applied which separate the air constituents of nitrogen and oxygen from one another according to the principle of pressure swing adsorption.
With this, the air fractionization is effected such that air is led through a molecular sieve at an increased pressure, wherein the easily adsorbable nitrogen accumulates on the surface of a molecular sieve whist the oxygen which may not be adsorbed on account of its low molecular size passes the molecular sieve.
The loading of the molecular sieve may be effected until achieving the condition of equilibrium. Its adsorption capacity is exhausted after this. In order to be able to carry out the process of air fractionization again, the regeneration of the loaded adsorber is required, i.e. a desorption of the adsorber, which is effected by a pressure reduction and subsequent flushing.
In order to be able to ensure an air fractionization with a quasi-continuous extraction of oxygen, one requires at least two molecular sieve chambers which are operated in parallel, of which in each case one is in the adsorption cycle whilst the other simultaneously regenerates.
For flushing the molecular sieve chamber to be regenerated, usually a part gas flow is taken from the product gas flow of the adsorbing molecular sieve chamber and led to the desorbing molecular sieve chamber.
A method for producing a product gas, in particular oxygen, from a feed gas mixture by way of pressure swing adsorption with which a part mass flow of the product gas is led to the desorbing molecular gas chamber for flushing is known from DE 693 23 481 T2. With this, the quantity of the supplied flushing gas is controlled in that the product gas concentration of the flushing gas is measured after the flushing of the desorbing molecular sieve chamber and the supply of flushing gas is stopped after achieving a certain product gas concentration.
The flushing of the desorbing molecular sieve chamber with known air fractionization installations on board aircraft is effected in that a part of the product gas flow is taken from the adsorbing molecular sieve chambers during their complete adsorption cycles and is led as a flushing gas to the desorbing molecular sieve chamber. At the same time the limitation of the flushing gas quantity is effected via a fixed throttle device.
With air fractionization for example at large flight altitudes in which the adsorption cycles are extended on account of the low air pressure prevailing there, this procedural manner leads to the fact that the flushing gas quantity which is made available for flushing the desorbing molecular sieve chamber is greater than is actually required. This reduces the efficiency of the air fractionization installation and has a negative effect on its energy requirement, size and weight.